In imaging methods as e.g. electro(photo)graphy, magnetography, ionography, etc. a latent image is formed that is developed by attraction of so called toner particles. Afterwards the developed latent image (toner image) is transferred to a final substrate and fused to this substrate. Toner particles are basically polymeric particles comprising a polymeric resin as main component and various ingredients mixed with said toner resin. Apart from colourless toners, which are used e.g. for finishing function or security purposes (e.g. when a clear fluorescent dye, pigment or phosphor is used), the toner particles comprise at least one black and/or colouring substances, e.g., coloured pigment, e.g. magenta, cyan or yellow.
In the beginning colour electro(photo)graphy was mostly used for producing coloured images (e.g. graphic arts, presentations, coloured books, dissertations, . . . ). When the process speed of producing digital coloured images increased, other more productive applications also came into the picture (direct mailing, transactional printing, packaging, labelprinting, security printing, . . . ). This means that after an electro(photo)graphy marking operation, the toner images further have to withstand some external factors applied during the subsequent treatments. The problems associated with multiple, superimposed layers of toner particles that are in one way or another fixed on a substrate are manifold, are not only with respect to image quality but also with respect to image stability and with respect to mechanical issues.
In 2003, in Deprez, Lode; Op de Beeck, Werner; Rosenberger, Karolina. “Digital production printing with UV-curable dry toners for paper and flexible packaging” IS&T's NIP19: International Conference on Digital Printing Technologies, Final Program and Proceedings, New Orleans, La., United States, Sep. 28-Oct. 3, 2003 (2003), 486-491) it has already been shown that the mechanical resistance of UV cured curable toner can be improved based on a Taber Abraser test.
In patent application US2007/0031751A1 a liquid developer is described which comprises an UV curable component to improve the adhesion to the substrate because liquid toner shows a limited adhesion onto paper. By including the UV curable component also the scratch resistance was improved.
In US 2005/0137278 a chemically produced toner is described which contains typically 5-10% of wax (in order to prevent hot offset) and a certain amount of UV crosslinking agent to improve the rub resistance measured with toluene. The wax compound in this application is encapsulated into the center of the toner particle.
The use of an additional layer on top of the colour image to improve the scratch resistance is described in U.S. Pat. No. 5,837,406 where a special reactive silicon oil is described.
The use of waxes to improve the scratch resistance is also known in the field. Examples are U.S. Pat. No. 6,733,940 where a MICR toner is described with a typical wax concentration of 1.5 to 5% and U.S. Pat. No. 5,928,825 where a grafted wax is described in a concentration of 2-15%.
In electrophotographic processes based on hot roller, fusing waxes are very often used to prevent hot offset. Documents like EP 1111474, US2006/0228639, US2005/0100808 and US2004/0142265 and IS&T NIP16 “Study on the effects of wax in polyester color toner” of Eida of KAO Corporation describe the use of waxes. From those documents can be learned that in order to be useful in hot roller fusing systems the amount of wax which is generally used is between 2-15%. In chemical produced toners the wax content is generally somewhat higher. When this amount of wax is present, the need for silicone oil in hot roller fusing can be prevented. From all those references only a general description for toners with an improved scratch resistance is found and also general teachings for the use of waxes in toner but a toner with a very high scratch resistance combined with very stable charging properties is still not attainable with the above teachings.